By: Rebecca Reilly
Historic buildings are often very aesthetically pleasing to the eye. However, since antiquated methods were used in their designs, the facades of these buildings are very difficult to preserve.
The mortar used to construct masonry structures has developed over time. Lime mortar was commonly used in older buildings. This type of mortar is significantly softer than the typical mortars containing Portland cement that is used today. Since Portland cement is often stronger than historic brick or stone units, utilizing this incompatible mortar on an older building can potentially cause brick units to deteriorate and spall. Building owners must always consider the age of their buildings before selecting materials to be installed.
Matching new brick units to existing brick masonry also poses a challenge. While brick masonry manufacturers can produce custom brick units to closely match the existing brick, these custom brick units are significantly more expensive and have a longer lead time. Building owners should factor in additional time in their project schedules for procurement of custom repair materials.
Historically, salt glazing was commonly used to manufacture terra cotta units. Since the salt glazing process emits sodium chloride and hydrochloric acid, anti-pollution laws no longer allow it to be performed. Today, in order to match new terra cotta units to existing ones, coating the terra cotta units is often required. Manufacturers of restoration materials have the ability to color match the coating to mimic the historic glazing.
Another challenge with repairing stone structures is obtaining stone matches. The original quarry where a building’s stone was sourced from may now be closed. Suppliers and installers must try to match the grain of the stone to ensure that the new blends with the old as it weathers.
Aside from matching the stone, other materials are available when performing stone replacement. Cast stone, which is concrete poured into molds, is a less expensive alternative. Additionally, fiberglass building elements can be fabricated to match existing stone elements. Fiberglass elements are beneficial because they are significantly lighter than stone units.